It is known that quantum computation devices (also referred to as “qubits”) need high precision magnetic bias signals to accurately set the operating point of the device. Control currents on the order of 10 milliAmps (mA) are required, with an accuracy of one part in a million, and the noise temperature of the control electronics must be low to avoid decohering the qubit. Because the qubit is operated at temperatures near 20 milliKelvin (mK), the usual way of directly coupling control signals to the quantum bit will heat the refrigerator and inject undesirable noise into the device. The simplest way to solve these problems is to use a thin film superconducting persistent current switch. Examples of such persistent current switches are disclosed in A. C. Leuthold, R. T. Wakai, G. K. G. Hohenwarter, and J. E. Nordman, “Characterization of a Simple Thin-Film Superconducting Switch,” IEEE Trans. Appl. Supercond., vol. 4, no. 3, pp. 181-183, 1994; and P. Balchandani, R. H. Torii, and R. Shile, “Thin-Film Persistent Current Switch,” IEEE Trans. Appl. Supercond., vol. 15, no. 3, pp. 3821-3826, 2005, the disclosures of which are incorporated by reference herein.
The standard switch design described in the existing literature involves joule heating a thin film superconducting niobium (Nb) line using a thin film heater which crosses the Nb line. To reduce the amount of power needed to operate the switch, the overlap area typically is 100 micrometers (μm)×100 μm. The amount of power needed to operate the switch is about 50 microWatts (μW).